Louis Lowry's novel The Giver Jonas is about a rigid, color-less, emotionless and dominated society where rules, jobs and even relationships are assigned by a group of Elders. In the novel Jonas, an 11 year old child, is the selected citizen that will receive the assignment of being the keeper of memories from prior to the time his dystopian society became what it is now. At 11 years of age, Jonas is now the most revered candidate to be the "Receiver" of the memories, while the old Receiver (who is now a very old man) would become "The Giver" of the memories that will enter Jonas's mind.
Chapter 8 of the novel focuses on the process of selection, and on how the Elders view the position of the Receiver. It is a huge deal, and they explain to Jonas what entails "proper" behavior. Among the citizens, to display "uncertainty" means that there is a degree of doubt on the rigid rules of the establishment. However, for an ELDER to display a dream of uncertainty means that the elder does not feel that the candidate for the role of Receiver is well-prepared for the task. Hence, if an Elder (in a process of solitude and meditation) suddenly doubts the candidate's abilities, the candidate would be "disqualified" or, as they say in the novel, "set aside". In some cases, immaturity is given as a reason, for which more time is allowed if a very young child is voted as candidate. However, Jonas was 11 years-old and displayed all the traits of a good Receiver; the elders never had any dreams of uncertainty against him.
Jonas was identified as a possible Receiver many years ago. We have observed him meticulously. There were no dreams of uncertainty.
Therefore, the worse that could happen after a dream of uncertainty is to be relieved from the opportunity to become a Receiver. Jonas had no issues with that because he had been observed from an early age and was deemed as the best candidate.